Probing Structure, Thermochemistry, Electron Affinity and Magnetic Moment of Dysprosium-doped Silicon Clusters DySi_n(n = 3～10) and Their Anions with Double-hybrid Density Functional Theory

The equilibrium geometries, electronic structures and electronic properties including adiabatic electron affinity（AEA）, vertical detachment energy（VDE）, simulated photoelectron spectroscopy, HOMO-LUMO gap, charge transfer, and magnetic moment for DySi_n（n = 3~10） clusters and their anions were systematically investigated by using the ABCluster global search technique combined with the B3 LYP and B2 PLYP density functional methods. The results showed that the lowest energy structure of neutral DySi_n（n = 3~10） can be regarded as substituting a Si atom of the ground state structure of Si_（n＋1） with a Dy atom. For anions, the extra electron effect on the structure is significant. Starting from n = 6, the lowest energy structures of DySi_n~？（n = 3~10） differ from those of neutral. The ground state is quintuplet electronic state for DySi_n（n = 3~10） excluding DySi_4 and DySi_9, which is a septet electronic state. For anions, the ground state is a sextuplet electronic state. The reliable AEA and VDE of DySi_n（n = 3~10） are reported. Analyses of HOMO-LUMO gaps indicated that doping Dy atom to silicon clusters can improve significantly their photochemical reactivity, especially for DySi_9. Analyses of NPA revealed that the 4 f electrons of Dy in DySi_4, DySi_9, and DySi_n~？ with n = 4 and 6~10 participate in bonding. That is, DySi_nbelongs to the AB type. The 4 f electrons of Dy atom provide substantially the total magnetic moments for DySi_n and their anions. The dissociation energies of Ln（Ln = Pr, Sm, Eu, Gd, Ho, and Dy） fromLn Sin and their anions were evaluated to examine the relative stabilities.

A Silicon Cluster Based Single Electron Transistor with Potential Room-Temperature Switching

We demonstrate the fabrication of a single electron transistor device based on a single ultra-small silicon quantum dot connected to a gold break junction with a nanometer scale separation. The gold break junction is created through a controllable electromigration process and the individual silicon quantum dot in the junction is deter- mined to be a Si 170 cluster. Differential conductance as a function of the bias and gate voltage clearly shows the Coulomb diamond which confirms that the transport is dominated by a single silicon quantum dot. It is found that the charging energy can be as large as 300meV, which is a result of the large capacitance of a small silicon quantum dot （-1.8 nm）. This large Coulomb interaction can potentially enable a single electron transistor to work at room temperature. The level spacing of the excited state can be as large as 10meV, which enables us to manipulate individual spin via an external magnetic field. The resulting Zeeman splitting is measured and the g factor of 2.3 is obtained, suggesting relatively weak electron-electron interaction in the silicon quantum dot which is beneficial for spin coherence time.

Influence of silicon cluster on epitaxial growth of silicon carbide

Precursor concentration dependences of growth rate, doping concentration and surface morphology have been investigated in the epitaxial growth of 4H-SiC（0001） epilayers with horizontal hot-wall CVD system using various precursor concentrations under constant C/Si ratio. Form the experimental data it is found that silicon cluster which is formed through gas phase nucleation plays an important role in controlling the doping concentration and epitaxial growth rate of the silicon carbide. It was observed that the concentration of silicon clusters cannot reach the equilibrium value in the process by using a low Sill4 concentration, and this phenomenon has not been reported by others.

CRITICAL SIZE OF COULOMBIC EXPLOSION FOR BIVALENT CATIONS OF SILICON CLUSTERS

Ⅰ. INTRODUCTIONSmall atomic dusters ranging from two to a few hundred atoms per cluster, also referred to as microclusters, attract great interest of physists, chemists and material scientists since 1980’s because of their peculiar behaviors and potential for industrial applications. The coulombic explosion is known as one of the remarkable properties inherent in microdusters. Experiments have shown that some positively charged dusters（cluster cations）, Mnm+

<i>Ab Initio</i>Molecular Orbital Calculation for Optical and Electronic Properties Evaluation of Small and Medium Size Silicon Nano-Clusters Found in Silicon Rich Oxide Films

In systems in atomic and nano scales such as clusters or agglomerates constituted of particles from a few to less than one hundred of atoms, quantum confinement effects are very important. Their optical and electronic properties are often dependent on the size of the systems and the way in which the atoms in these clusters are bonded. Generally, these nano-structures display optical and electronic properties significantly different of those found in corresponding bulk materials. Silicon agglomerates found in Silicon Rich Oxide (SRO) films have optical properties, which have reported as depended directly on nano-crystal size. Furthermore, the room temperature photoluminescence (PL) of Silicon Rich Oxides (SRO) has repeatedly generated a huge interest due to their possible applications in optoelectronic devices. However, a plausible emission mechanism has not yet widespread acceptance of the scientific community. In this research, we employed the Density Functional Theory with a functional B3LYP and a basis set 6 - 31G* to calculate the optical and electronic properties of small (six to ten silicon atoms) and medium size clusters of silicon (constituted of eleven to fourteen silicon atoms). With the theoretical calculation of the structural and optical properties of silicon clusters, it is possible to evaluate the contribution of silicon agglomerates in the luminescent emission mechanism experimentally found in thin SRO films.

STRUCTURE EFFECTS OF SILICON AND CARBON BY CLUSTER MASS SPECTRA

Microclusters from different structures of silicon and carbon are studied by SIMS under UHV conditions in the mass range below M=200. The sputtered mass spectra of ions Sin+, Cn+ and Cn were obtained from the 10 keV O2+ primary beam bombardment. Comparisons of each spectrum in each group have shown the strong structure effects on the cluster patterns. A brief discussion on the results has been given.

Parity Alternation of Silicon-doped Ternary Cationic Clusters HC_nSi_2^+(n=1～9)

Systematic study on the electronic/geometrical structures and the parity alternation effect of silicon-doped ternary cationic clusters HCnSi2＋（n = 1 ~9） have been carried out at the coupled cluster level. The ground-state （G-S） isomers of the clusters have been defined. The C, chains of the G-S isomers display polyacetylene-like structures. The even-n cations are more stable than the odd-n ones. Such a trend of even/odd alternation has been elaborated based on concepts of the bond character, atomic charge, incremental binding energy, ionization potential, proton affinity and fragmentation energies of the systems. The findings accord with the relative intensities of HC,,Si2＋ species recorded in the related mass spectrometric experiments.

Ag_(n-1)Si(n=5-10)团簇结构与性质研究

采用密度泛函理论研究了Ag_(n-1)Si团簇(n=5-10)的几何结构和物理性质.首先得到体系最低能量结构,其中Ag5Si和Ag7Si团簇的结构比之前研究中结构能量更低.通过分析相应结构的能隙,平均结合能,二阶能量差可以发现Si原子的加入可以加强团簇结构稳定性,使团簇更加紧凑.在团簇尺寸n=5-10的范围里,拥有八个价电子的Ag4Si团簇在以上三个方面都显示出非常稳定的特点.通过分析Ag_(n-1)Si团簇(n=5-10)的差分电荷发现,电荷的转移主要发生在Si原子与其相邻的Ag原子之间,Si原子和附近的Ag原子之间产生了强烈的共价相互作用,是团簇稳定性增强的重要原因.

Structural and bonding properties of ScSi_n^-(n=2～6) clusters:photoelectron spectroscopy and density functional calculations

Anion ion photoelectron spectroscopy and density functional theory （DFT） are used to investigate the electronic and structural properties of ScSin （n = 2 - 6） clusters and their neutrals. We find that the structures of ScSin^- are similar to those of Sin＋1^-. The most stable isomers of ScSin^- cluster anions and their neutrals are similar for n=-2, 3 and 5 but different for n=4 and 6, indicating that the charge effect on geometry is size dependent for small scandiumsilicon clusters. The low electron binding energy （EBE） tails observed in the spectra of ScSi4,6^- can be explained by the existence of less stable isomers. A comparison between ScSin and VSin clusters shows the effects of metal size and electron configuration on cluster geometries.

First-Principles Calculations for Structures and Melting Temperature of Si6 Clusters

We investigate the structures and the melting temperature of the Si6 cluster by using the first-principles pseudopotential method in real space and Langevin molecular dynamics. It is shown that the ground structure of the Si6 cluster is a square bipyramid, and the corresponding melting temperature is about 1923 K. In the heating procedure, the structures of the Si6 cluster change from high symmetry structures containing 5-8 bonds, via prolate structures containing 3-4 bonds, to oblate structures containing 1-2 bonds.

Cluster structure prediction via CALYPSO method

Cluster science as a bridge linking atomic molecular physics and condensed matter inspired the nanomaterials development in the past decades, ranging from the single-atom catalysis to ligand-protected noble metal clusters. The corresponding studies not only have been restricted to the search for the geometrical structures of clusters, but also have promoted the development of cluster-assembled materials as the building blocks. The CALYPSO cluster prediction method combined with other computational techniques have significantly stimulated the development of the cluster-based nanomaterials. In this review, we will summarize some good cases of cluster structure by CALYPSO method, which have also been successfully identified by the photoelectron spectra experiments. Beginning with the alkali-metal clusters, which serve as benchmarks, a series of studies are performed on the size-dependent elemental clusters which possess relatively high stability and interesting chemical physical properties. Special attentions are paid to the boron-based clusters because of their promising applications. The NbSi12 and BeB16 clusters, for example, are two classic representatives of the silicon-and boron-based clusters, which can be viewed as building blocks of nanotubes and borophene. This review offers a detailed description of the structural evolutions and electronic properties of medium-sized pure and doped clusters, which will advance fundamental knowledge of cluster-based nanomaterials and provide valuable information for further theoretical and experimental studies.

Study on the defect-related emissions in the light self-ion-implanted Si films by a silicon-on-insulator structure

This paper reports that the Si＋ self-ion-implantation are conducted on the silicon-on-insulator wafers with the 2SSi＋ doses of 7 ×1012, 1 × 1013, 4 × 1013, and 3× 1014 cm-2, respectively. After the suitable annealing, these samples are characterized by using the photoluminescence technique at different recorded temperatures. Plentiful emission peaks are observed in these implanted silicon-on-insulator samples, including the unwonted intense P~ band which exhibits a great potential in the optoelectronic application. These results indicate that severe transformation of the interstitial clusters can be manipulated by the implanting dose at suitable annealing temperatures. The high critical temperatures for the photoluminescence intensity growth of the two signatures are well discussed based on the thermal ionization model of free exciton.

Boron implanted emitter for n-type silicon solar cell

The effects of ion doses on the properties of boron implanted Si for n-type solar cell application were investigated with doses ranging from 5×10^14cm^-2 to 2×10^15cm^-2 and a subsequent two-step annealing process in a tube furnace.With the help of the TCAD process simulation tool, knowledge on diffusion kinetics of dopants and damage evolution was obtained by fitting SIMS measured boron profiles. Due to insufficient elimination of the residual damage, the implanted emitter was found to have a higher saturation current density（J0e） and a poorer crystallographic quality. Consistent with this observation, V oc, J sc, and the efficiency of the all-implanted p^＋–n–n^＋solar cells followed a decreasing trend with an increase of the implantation dose. The obtained maximum efficiency was 19.59% at a low dose of 5×10^14cm^-2. The main efficiency loss under high doses came not only from increased recombination of carriers in the space charge region revealed by double-diode parameters of dark I–V curves, but also from the degraded minority carrier diffusion length in the emitter and base evidenced by IQE data. These experimental results indicated that clusters and dislocation loops had appeared at high implantation doses, which acted as effective recombination centers for photogenerated carriers.

The Cluster Fe₂Si₁₈as the New Quantum Bit System

Multiconfiguration quantum chemical calculation of geometry and electron properties of Fe2Si18 cluster indicates on the predictable change of spin states as a function of the excitation energy beginning from ground state with the total spin S = 4. The charges on the two Fe atoms are quite different as well as the charge distribution on the surrounding Si atoms. Nevertheless the total dipole moment of the cluster is a monotonically decreasing function of the excitation energy and it reaches practically zero value in the first singlet state in which the cluster represents a new version of a quibit system.

Dielectric layer-dependent surface plasmon effect of metallic nanoparticles on silicon substrate

The electromagnetic interaction between Ag nanoparticles on the top of the Si substrate and the incident light has been studied by numerical simulations. It is found that the presence of dielectric layers with different thicknesses leads to the varied resonance wavelength and scattering cross section and consequently the shifted photocurrent response for all wavelengths. These different behaviours are determined by whether the dielectric layer is beyond the domain where the elcetric field of metallic plasmons takes effect, combined with the effect of geometrical optics. It is revealed that for particles of a certain size, an appropriate dielectric thickness is desirable to achieve the best absorption. For a certain thickness of spacer, an appropriate granular size is also desirable. These observations have substantial applications for the optimization of surface plasmon enhanced silicon solar cells.

Structures and electronic properties of Si_m N_(8-m)(0

The geometries, electronic structures and related properties of SimN8-m（0 〈 m 〈 8） clusters are studied using density functional theory （DFT） with hybrid functional B3LYP. The calculated results reveal several trends. For any stoichiometric clusters, the lowest energy isomers with an alteration of N and Si atoms are favourable in energy if the numbers of Si and N atoms are large enough to form ... Si N-Si-N... alternative chains. The bond lengths of single Si-N bonds are very close to the corresponding values of the bulk and other SiN clusters. The geometries for N-rich and Si4N4 clusters are planar structures, but three-dimensional structures are favourable in energy for Si-rich clusters. With the increase of m, the isotropic polarizability and average polarizability increase, the total binding energies generally decrease, the HOMO-LUMO gap and vertical ionization potential oscillate with increasing number of valence electrons, and their values with even valence electrons are larger than those with odd valence electrons. The atomic charges, IR and Raman properties are also reported.

Study of Quantitative and Qualitative Characteristics of Nickel Clusters and Semiconductor Structures

The possibility of building of clusters of impurity atoms of Ni in silicon and controlling their parameters is currently investigated in the present research article. Our group develops a special technique for doping, the so-called “low-temperature doping” of semiconductors. This method of doping is based upon the diffusion process which is carried out in stages by gradually increasing temperature ranging from room temperature to the diffusion temperature.

小尺寸锂硅团簇SinLi （n=1-10）的理论研究

采用密度泛函理论研究了锂硅团簇SinLi （n=1-10）的结构、稳定性和电子性质。计算结果表明锂原子处于硅团簇表面并且位于硅原子的桥位更稳定。SinLi团簇结合能表明锂原子的嵌入提高了硅团簇的稳定性。另外, 锂原子的结合能说明锂与硅团簇的相互作用随着硅团簇尺寸的减小而增强, 由此得到锂离子电池硅基负极材料嵌锂过程粉末化的一个重要原因。锂硅团簇的电离势、电子亲和势、化学势与能隙均表明Si4Li与Si7Li更容易失去一个α电子形成阳离子团簇。

过渡金属原子钴掺杂硅团簇CoSi_(6～9)的密度泛函理论研究

利用密度泛函理论对CoSi_n(n=6～9)中性团簇的几何结构演化和电子结构性质进行研究,结果表明Co掺杂硅团簇的最小笼状尺寸是n=9,其中Co原子被扭曲状的Si_9棱柱包拢.CoSi_8团簇由于存在多个能量相近的异构体,导致团簇的吸附活性降低.自然电荷布局分析表明对于笼状的Co@Si_9团簇,其电荷主要分布在外围的硅笼,内部的Co原子通过spd杂化与外部硅笼成键,这保持了笼状团簇的稳定.